1. Field of the invention
The present invention is in the field of propulsion systems for rotary wing aircraft and in particular is an apparatus for improving the autorotation performance of a helicopter operating within its "Dead Man Zone".
2. Description of the Prior Art
The lift capacity of a helicopter is totally dependent upon the rotary movement of the rotor blades and a helicopter does not, per se, have any glide characteristics which typify many fixed wing aircraft. Thus, in the event of a main propulsion plant failure in a helicopter, rotor speed drops when power is no longer delivered to the rotor system. Lift developed by the rotor system is thusly, in part, dependent upon rotor speed. At high enough altitudes, failure of the main propulsion plant will allow the pilot to successfully enter an autorotation mode wherein the descent of the helicopter is used to transfer power into the rotor system, thereby rotating the rotor blades, providing lift and thereby lessening the rate of descent. In a properly designed rotor system, a helicopter will be able to survive a hard landing in the autorotation mode but only if enough energy is coupled into the rotor system during descent. Due to the limitations of prior art helicopter designs, sufficient energy cannot be coupled into the rotor system unless the helicopter is at or above a minimum altitude at the time of power failure.
However, many of the flight applications for helicopters are and must be conducted at low altitudes which are well below the minimum altitude for safe autorotation. These altitude zones, commonly called "dead man zones", represent altitudes below which power failure in a single engine helicopter will generally result in a crash landing.
In military applications, flight operations are typically conducted in the dead man zones to reduce target vulnerability and maintain surprise. However, it is also within this altitude zone that damage to a helicopter in a combat engagement is most prevalent. Therefore, in military operations, a high proportion of aircraft loss is caused by loss or partial loss of the main propulsion system in the low altitude zone followed by the inability of the helicopter to autorotate to an undamaged landing.
Therefore, what is needed is some means which will allow a rotary aircraft to autorotate to an undamaged landing in the dead man zone where, for any reason, a loss or substantial disability is suffered by the main propulsion system.